As presented in Patent Document 1, two three-phase motors, two inverter circuits connected respectively to the three-phase motors, and a voltage step-up/step-down circuit for supplying electric power to the inverter circuits are mounted in a conventional hybrid automobile. The voltage step-up/step-down circuit is formed by a chopper circuit, and performs a voltage step-up conversion and a voltage step-down conversion on an input voltage supplied from a high-voltage battery to thereby generate a P-phase potential and an N-phase potential which are necessary for the inverter circuits. For example, one of the two three-phase motors is a motor for driving wheels, and the other is a motor for electric power regeneration.
A control board on which is formed a circuit for driving the two inverter circuits and the voltage step-up/step-down circuit is further mounted in the conventional hybrid automobile. The control board is referred to hereinafter as a vehicle-mounted motor driving control board. This vehicle-mounted motor driving control board is comprised of a single printed circuit board, and is connected to a semiconductor module including two inverter circuits and a voltage step-up/step-down circuit.
The vehicle-mounted motor driving control board includes two inverter circuit driving circuits which are circuits for driving the two inverter circuits, respectively, and a voltage step-up/step-down driving circuit which is a circuit for driving the voltage step-up/step-down circuit.
The vehicle-mounted motor driving control board further includes a power supply circuit for supplying a constant DC voltage to the two inverter circuit driving circuits and to the voltage step-up/step-down driving circuit. This power supply circuit converts an input voltage supplied from a battery into a control voltage (output voltage) necessary for the two inverter circuit driving circuits and the voltage step-up/step-down driving circuit.